The invention relates to an apparatus for producing aerosols from liquids, also known as aerosol or particle generators.
Aerosol or particle generators hereinafter called particle generators are very widely used. Generally such a generator includes an atomiser mounted in a vessel, which is provided with a particle or aerosol outlet.
Aerosol or particle gnerators for example are used in air humidifiers, powder production, vacuum drying and inhalation therapy, furthermore in experimental aerodynamics if tracer or light scattering particles are to be fed into a wind tunnel for laser anemometry.
The generation principle used for liquid particles can be ultrasonic, the condensation method or pneumatic atomising. The main operating parameters of a particle generator are the generation rates and the spectrum of particle size with the average diameter.
The use of a generation principle for one of the above depends upon the required particle size and the infeed rate. For inhalation therapy for example droplets of approx. 2 .mu.m diameter are required at an infeed rate of approx. 10.sup.6 s.sup.-1, two of the conditions fulfilled well by ultrasonic atomisation. In laser anemometry the necessary particle diameter depends upon the slip of the particles in the flow. With very large flow vector gradients, as for example in compression shocks, a diameter down to approx. 0.2 .mu.m is required. In a relatively regular flow the particle diameter may reach approx. 2 .mu.m. At higher flow velocities larger particles are required due to the shorter duration of the particles in the laser beam for producing the scattering light photon index. If the particle size cannot be further increased due to the decreasing of slip in the flow then the laser beam power must be increased. The particle size affects the mechanisms in the particle generator due to the coagulation effect.
In smaller wind tunnel systems the particle infeed rate produces no problems but can do in larger plants. Existing generators cannot achieve very high generation rates with very small particle sizes of around 1 .mu.m and less, as are for example desirable for fuel preparation by spraying.